This invention relates to color picture tubes having tension masks, and particularly to a tube having means for connecting a tension mask, that is made of a material having a relatively low coefficient of thermal expansion material, to a support frame, that has a significantly higher coefficient of thermal expansion.
A color picture tube includes an electron gun for generating and directing three electron beams to the screen of the tube. The screen is located. on the inner surface of a faceplate of the tube and is made up of an array of elements of three different color emitting phosphors. A color selection electrode, which may be either a shadow mask or a focus mask, is interposed between the gun and the screen to permit each electron beam to strike only the phosphor elements associated with that beam. A shadow mask is a thin sheet of metal, such as steel, that is usually contoured to somewhat parallel the inner surface of the tube faceplate.
One type of color picture tube has a tension mask mounted within a faceplate panel thereof. In order to maintain the tension on the mask, the mask must be attached to a relatively massive support frame. Although such tubes have found wide consumer acceptance, there is still a need for further improvement, to reduce the weight and cost of the mask-frame assemblies in such tubes.
It has been suggested that a lighter frame could be used in a tension mask tube if the required tension on a mask is reduced. One way to reduce the required mask tension is to make the mask from a material having a low coefficient of thermal expansion, such as Invar. However, a mask from such material would require a support frame of a material having a similar coefficient of thermal expansion, to prevent any mismatch of expansions during thermal processing that is required for tube manufacturing, and during tube operation. Because the metal materials that have low coefficients of thermal expansion are relatively expensive, it is relatively costly to make both the mask and frame out of identical or similar low expansion materials. Therefore, it is desirable to use the combination of a low expansion tension mask with a higher expansion support frame. However, a thermal expansion mismatch between mask and frame often results in mask wrinkles following thermal processing, which may involve temperatures as high as 450xc2x0 C., such as during frit sealing. One solution to deal with this expansion mismatch is to individually weld each mask strand to the frame. It has been found that such individual welding of the strands of a tension mask to a frame causes the mask strands to become misaligned, when existing roller welders are used.
The present invention addresses a need for a solution to the problem, of attaching a tension mask to a frame, that exists when there is a substantial mismatch in coefficients of thermal expansion between a tension mask and its support frame.
The present invention provides an improvement in a color picture tube having a tension mask supported by a support frame mounted within the tube. The mask has a significantly lower coefficient of thermal expansion than the frame. The frame has two substantially parallel cantilevered members, each member having a distal edge to which the tension mask is attached. At least one of the distal edges has two sections separated by a gap therebetween. The two sections include an inner section and an outer section. The mask is glued to the inner section and is welded to the outer section.